1. Field of the Invention
The present invention relates to a plasma treating method and apparatus therefor, and more particularly to a plasma treating method and apparatus therefor which is suitable for treatments such as etching treatment, film-forming treatment and the like of a specimen such as the substrate of a semiconductor element utilizing a plasma while cooling the specimen to a low temperature less than 0.degree. C.
2. Description of the Prior Art
Techniques for cooling a specimen such as the substrate of a semiconductor element to a low temperature less than 0.degree. C. and applying a plasma treatment thereto have been known, for example, from Japanese Patent Laid-Open No. 158627/1985, Japanese Patent Laid-Open No. 240635/1986 and the like, in which a specimen table on which a specimen is placed is cooled by, for example, liquid nitrogen or the like, the specimen is cooled to a low temperature less than 0.degree. C. through the thus cooled specimen table, and the specimen is subjected to etching treatment utilizing a plasma.
In the plasma treating techniques disclosed, for example, in Japanese Patent Laid-Open No. 158627/1985 and Japanese Patent Laid-Open No. 240635/1986, an exposed surface within a treating chamber which is exposed to an atmosphere at which specimen is treated (hereinafter referred to as a pressure-reduced atmosphere exposed surface) except a specimen place surface of a specimen table on which specimen is placed is also cooled to a low temperature less than 0.degree. C. similar to the specimen place surface of the specimen table. When the exposed surface is cooled to a temperature less than a dew point of a treating gas under the pressure-reduced atmosphere or reactive product produced when a specimen is treated (hereinafter referred to as an atmospheric gas), the adsorption of the atmospheric gas on the exposed surface is unavoidable. This poses problems as follows:
(1) When the growth of an adsorbed material progresses on the exposed surface within the treating chamber of the specimen table, the adsorbed material is peeled off in the form of a solid from the exposed surface, which is then formed into a source of foreign matter which constitutes an adverse affect such as the lowering of yield of the specimen.
(2) When the growth of an adsorbed material progresses on the exposed surface within the treating chamber of the specimen table, the adsorbed material is peeled off in the form of a solid from the exposed surface. This gives rise to troubles such as a blinding of an exhaust device which reduces pressure and exhausts the interior of the treating chamber.
(3) Sublimation of the adsorbed material on the exposed surface within the treating chamber of the specimen table and discharge operation of the sublimed material outside the treating chamber are separately required.
(4) When the treating chamber is opened in the state wherein the adsorbed material is present, sublimation of the adsorbed material occurs and discharge of gases outside occurs, which is dangerous for an operator.
(5) When the treating chamber is opened in the state wherein the adsorbed material is present, if the adsorbed material is a chloric-system adsorbed material, the material is reacted with moisture in air to produce a hydrochloric acid, which forms a corrosion environment to possibly damage the apparats.
(6) The adsorption of the treating gases on the exposed surface lowers the pressure within the treating chamber which is under the pressure-reduced atmosphere. Because of this, it becomes difficult to control the pressure within the treating chamber to a predetermined treating pressure, failing to treat the specimen in a satisfactory manner.